1. Field of the Invention
This invention relates to a rear projection display that modulates a light emitted from a light source lamp to thereby display a displayed on a screen.
2. Description of the Related Art
As a rear projection display of this kind, the present assignee has already proposed a rear projection display in Japanese Laid-Open Patent Publication (Kokai) No. 2002-139794. This rear projection display is comprised of light-generating means including a light source formed by a high-pressure mercury-vapor lamp, a metal halide lamp, or the like, for emitting a red light, a green light, and a blue light, light-modulating devices for modulating the respective lights emitted by the light-generating means, projection optical systems formed e.g. by lenses for magnifying the respective lights modulated by the light-modulating devices, reflecting mirrors for reflecting the lights magnified by the projection optical systems, and a rear projection screen that receives lights reflected by the reflecting mirrors, for projection display of various types of display screens. In the rear projection display, when a power switch is operated by a user to turn on the power, the light-generating means starts to be energized to cause the light source to illuminate. Then, the lights emitted by the light-generating means are modulated by the light-modulating devices, and projected onto the screen from a rear surface side thereof via the projection optical systems and the reflecting mirrors. Thus, a display screen dependent on-light modulations by the light-modulating devices is displayed on the screen.
However, from the study of the above described rear projection display, the present inventor found out the following points for improvement: In the rear projection display, a high-pressure mercury-vapor lamp, a metal halide lamp, or the like, is employed as the light source. In the case of the high-pressure mercury-vapor lamp or the metal halide lamp, after the energization thereof is started, it takes a time period ranging from several tens of seconds to several minutes, before the luminance thereof is increased to such a level that the display can be displayed by projection. Therefore, for some time after the power switch was operated by the user, no displayed appears on the screen. Thus, in the rear projection display, when the power switch is operated, it is difficult for the user to recognize whether or not the rear projection display has accepted the operation of the power switch, so that improvement on this point is desirable. In this case, it can be contemplated to configure the rear projection display such that the high-pressure mercury-vapor lamp or the like as the light source for projection display is replaced by a lamp (e.g. a halogen lamp) whose luminance level increases at a fast rate at the start of illumination, thereby enabling projection display of a display screen immediately after the power switch is operated. However, this kind of lamp whose luminance level rises at a fast rate at the start of illumination is generally lower in luminance level than the high-pressure mercury-vapor lamp or the like, which makes it difficult to clearly display a display screen by projection. On the other hand, it can be also contemplated to configure the rear projection display such that the two lamps of a high-pressure mercury-vapor lamp and a halogen lamp, for example, are arranged for simultaneous illumination at power on, and a light emitted from the halogen lamp is used for projection display until the luminance level of a light emitted by the high-pressure mercury-vapor lamp becomes high enough. However, this configuration necessitates provision of prisms, reflecting mirrors, etc., for guiding the respective lights emitted by the two lamps to the light-modulating devices and projection optical systems. This brings about the problem of the increased manufacturing costs of the rear projection display owing to the additional costs of these components and the increased size of the entire display.